1. Technical Field
The present invention relates to crystal growing in general, and in particular to a method and apparatus for growing single crystals of metals. Still more specifically, the present invention relates to a method and apparatus for growing large single-crystal metals via plastic straining.
2. Description of Related Art
Polycrystalline metals often have limited high-temperature creep resistance and low-temperature brittleness due to the presence of grain boundaries. In contrast, single-crystal metals often have better mechanical properties due to the absence of grain boundaries. Thus, for many applications, single-crystal metals are preferred over polycrystalline metals.
Current technologies for producing single-crystal metals are primarily based on one of following five basic processes:                (a) thin-film single crystals slowly grown through various deposition processes (currently used by the semiconductor industry);        (b) bulk single crystals slowly grown from a molten metal using a seed crystal (i.e., the Czochralski process, the Bridgman process, or a variation of the Czochralski and the Bridgman processes);        (c) bulk single crystals slowly produced by zone melting (also known as the floating-zone method) that uses a moving heating zone to perform localized melting of polycrystalline metal followed by solidification;        (d) bulk single crystals produced by zone annealing, in which a heating zone is passed along polycrystalline metal to locally produce recrystallization, grain growth, and boundary migration of a single grain; and        (e) bulk single crystals of refractory metals produced by alloying with oxide-forming elements followed by deformation at low temperatures, and followed by annealing at temperatures over 1800° C.All of the above-mentioned processes generally have a very slow production rate, and for those processes that can yield large single crystals, such as processes (b)-(e), very high temperatures are typically required during production. Consequently, it is desired to provide an improved method for producing large single-crystal metals with faster production rates and at lower temperatures than those in the above-mentioned processes.        